Information playback systems frequently utilize a stylus for reading signals from the surface of an information record, typically a plastic disc, that contains stored video and audio information. In some systems the information record has a fine spiral groove to guide the tip of a stylus that contains a thin electrode. In these systems the stylus is typically made from natural or synthetic diamond by several critical shaping and lapping processes, normally referred to as micromachining. The stylus tip is tapered to form the prow of the tip, and is also lapped to form a keel having a V-shaped shoe for its bottom portion. This keel-shaped tip has a shoe length of about 3 to 5 micrometers and a thickness of about 2 micrometers. These micromachining steps are normally performed while the stylus is mounted on an arm attached to a cartridge, wherein the arm is capable of flexible movement with respect to the cartridge.
In manufacturing stylus tips for use in such video disc playback systems, after each micromachining step the tip of the diamond stylus is inspected with a high-power optical microscope having 1000.times. to 1500.times. magnification. Since the stylus tip is about 2.times.5 micrometers in size and the depth of focus of the microscope is about 1 micrometer, the problem of locating the stylus tip in the field of view of the microscope is severe. Untrained operators may require more than 1 hour to perform this task, while even highly skilled operators still require 1/2 to 1 minute normally. Moreover, there is considerable danger that the sharp stylus tip will accidentally touch the high-power microscope objective, thereby ruining an expensive element.
The system described below is intended to simplify the stylus inspection technique, while also avoiding the danger of accidentally damaging the microscope objective. Another advantage is the fact that oil-immersion optics can be used to give better, brighter, higher-resolution images of the stylus tip while avoiding the need to frequently clean and reoil the microscope objective. The present invention provides a novel method and apparatus for rapidly positioning the tip of a stylus mounted on a flexible arm attached to a cartridge.